[vh1] use standard sort (#2072)

youtube_dl/extractor/mtv.py

@@ -80,8 +80,7 @@ class MTVServicesInfoExtractor(InfoExtractor):
                                 })
             except (KeyError, TypeError):
                 raise ExtractorError('Invalid rendition field.')
-        # worst format is expected to be first and best one last
-        formats.sort(key=lambda x: int(x['format_id']))
+        self._sort_formats(formats)
         return formats
 
     def _get_video_info(self, itemdoc):